Desktop Survival Guide
by Graham Williams

Arrow Axes

The par function in R can be used to fine tune characteristics of a plot. Here we add arrows to the axes. For many more arrow options see the p.arrows function in the sfsmisc package.

In the example here, par("usr") is used to identify the bounds of the plot, and these are then employed to draw axes with arrows. The arrows function takes a starting point and an ending point for the line to be drawn. The code=2 selects the type of arrow head to draw and the xpd=TRUE ensures the arrows are not cropped to the default size of the plot (the plot region).

Image rplot-iris-arrows

plot(Petal.Length, Petal.Width, axes=FALSE)
u <- par("usr")
arrows(u[1], u[3], u[2], u[3], code=2, xpd=TRUE)
arrows(u[1], u[3], u[1], u[4], code=2, xpd=TRUE)

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